The goal of this K08 application is provide the essential skills and experience that will allow the Principal Investigator to become a successful, independent physician-scientist. This proposal seeks to define a role for activated protein C (ARC) and its receptor, the endothelial protein C receptor (EPCR) in the pathophysiology and treatment of acute lung injury (ALI). Most commonly seen in the setting of sepsis, all is a devastating and complex inflammatory syndrome marked by increased vascular permeability resulting in tissue edema and organ dysfunction. Unfortunately, recent insights into the mechanisms of ALI have not translated into improved therapy and treatment is largely supportive. Moreover, mechanical ventilation (MV), the bedrock of ALI management, can contribute to sepsis-induced lung injury, a phenomenon referred to as ventilator associated lung injury (VALI). ARC has been proven to reduce mortality in sepsis, yet a beneficial effect in ALI without sepsis remains to be determined. Moreover, the exact mechanisms through which ARC reduces mortality in patients with severe sepsis (and potentially ALI) remain undefined. Clearly, a better understanding of the biology of ARC is needed. Preliminary data generated by the Principal Investigator demonstrate that APC reduces endothelial permeability in vitro and we hypothesize that APC, via EPCR, protects against the mechacal stress injury seen in VALI. SA #1 will focus on cyclic stretch, a reliable in vitro model of VALI. Using measures of endothelial resistance, protein biochemistry, siRNA, RT-PCR, confocal microscopy, biotinylation and Western blotting will define the role of EPCR in cyclic stress- and APC-induced signaling and cytoskeletal reorganization. In SA #2, using transgenic EPCR-deficient and over-expressing mice, we will characterize the role of EPCR in a well established, murine model of VALI. In SA #3, we will define the efficacy of APC treatment in VALI, again using EPCR transgenic mice to determine the role of EPCR in APC-mediated protection. Acute lung injury (ALI) is a devastating illness which kills over 70,000 people each year. While there have been some recent advances, treatment is largely supportive and unsuccessful. The purpose of this study is to define the role of activated protein C (APC) and its receptor, the endothelial protein C receptor, in the ALI and determine the efficacy of APC in the treatment of ALI. (End of Abstract)